There are three keywords that can appear in a fixture.

|null|''is replaced with a true null when used in a string column''|
|blank|''is replaced with an empty string when used in a string column''|
|error|''Turns the cell red if there were no errors.  Turns the cell green if there was an exception.''|

Click [[here][.FitNesse.SuiteAcceptanceTests.SuiteFixtureTests.SuiteGeneralFixtureSpec.TestBlankAndNullCells]] to see the acceptance tests for null and blank.